The present invention relates to a new and improved generating method and apparatus for grinding cylindrical gears possessing essentially involute-shaped tooth profiles, by means of two substantially plate-shaped or dished grinding wheels which machine a right tooth flank and a left tooth flank by means of practically point-like contact zones dispositioned at their related lateral edge, and wherein there is carried out between the gear and both grinding wheels a to-and-fro generating motion related to the base cylinder or circle of the gear.
According to a prior art method of this species (see e.g. MAAG Taschenbuch, Zurich 1963, Pages 259-268), both of the contact zones are always disposed in a tangential plane at the base cylinder of the workpiece. Due to the generating motion both of the grinding wheels produce an involute tooth profile by means of their contact zones. With this operation, as a general rule, there cannot be avoided a certain over-run of the generating motion, in order to make certain that the contact zones for sure wipingly contact the entire tooth profile. This over-run is present by virtue of the fact that one of both grinding wheels or disks, following the grinding of the tooth tip of a tooth flank, is retracted so as to be spaced from the tooth during the further generating motion, in other words so-to-speak grinds "air," whereas the other grinding wheel still machines the tooth root portion of another tooth flank. Such over-run must be accepted in practically all situations, since it is extremely seldom and only incidentally happens during the design of the gear teeth that there is simultaneously machined a tooth tip and a tooth root by a respective grinding wheel. Consequently, it was heretofore necessary to work with a generating stroke larger than that which corresponds to the actual length of the tooth profile.